Radio beam and receiving device for blind landing of aircraft



Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LANDING OF AIRCRAFT Filed Aug.5, 1932 5 Sheets-Sheet l Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LAND ING 0F AIRCRAFT FiledAug.' 5, 1932 5 Sheets-Sheet 2 FIGURE 2.]

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' Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LANDING OF AIRCRAFT Filed Aug.5, 1932 5 Sheets-Sheet s FSGUIZE 4 [mAeNn-uoz SCALE. m ARB'TRARY uun's]FIGURE 5 Aug. 23, 1938.

F. W. DUNMORE RADIO BEAM AND nscmvme DEVICE FOR BLIND LANDING 0FAIRCRAFT Filed Aug. 5, 1932 5 Sheets-Sheet 4 I new 00 com I com PatentedAug. 23, 1938- -RADIO BEAM AND RECEIVING DEVICE FOR. BLIND LANDING OFAIRCRAFT Francis W. Dunmore, Washington, D. 0., assignorto theGovernment oi the United States, as represented by the Secretary ofCommerce Application August 5, 1932, Serial No. 627,625

16 Claims.

(Granted under the m of March 3, 1883, as amended April 30, 1928; 370 0.G. 757) The invention described herein may be manufactured and used byor for the Government of the United States for governmental purposesonly without the payment of any royalty thereon.

This invention relates to the use of radio beams or landing aircraft.

The practicability of the use of directional radio as an aid topoint-to-point flying has been demonstrated by over three years ofservice given by the radio range-beacon system on the fixed airways. Bymeans of this system the pilot can keep accurately on his course, knowapproximately the points he is flying over, and proceed unerringly tohis destination. Scheduled air transport operation is thus immeasurablyaided; many flights are made which could not possibly be made withoutthe use of radio direction facilities. Nevertheless, interruption ofscheduled flying is still the rule whenever the landing field lies in anarea completely inclosed by fog. The results secured by the development01' instrument flying and radio navigational aids are then nullifiedthrough the lack of means for safe landing at the-desired destination,under conditions of poor visibility.

Any system of aids permitting the landing of aircraft under conditionsof zero visibility must give the pilot information of the position ofhis airplane in three dimensions as he approaches and reaches the pointof landing. Means are available for orienting the landing airplane alongthe proper runway and also furnishing the pilot an indication of hisapproximate position along that runway (see Air Commerce Bulletin", vol.2, .No. 4, August 15, 1930, and Bureau of Standards Journal of Research,October 1930, vol. 5, paper 238). These do not form a portion of myinvention except as they areused in combination with the landing beam toproduce the new result of this invention. All that remains necessary forlanding aircraft when the airport is completely inclosed by fog is togive the pilot vertical guidance. 1

The object of my invention, therefore, is to providea radio beam systemwhereby a pilot is furnished with the necessary vertical guidance topermitthe landing of an airplane under conditions of poor or novisibility. The transmitting portion of the system comprising myinvention .consists of an ultra-high frequency beam directed at a smallangle above the horizontal, this angle and the degree of directivity ofthe beam being so adjusted that a predetermined line of constant fieldintensity on the under side of the beam will mark out just the propergliding path 5 clearing all obstructions and convenient for landing. Thebeam is oriented so that its horizontal protection or trace is along thelanding runway.

-As noted in the foregoing, details of a system radiations in order toeffect a safe landing also 15 form a portion or my invention. 'Briefly,this equipment comprises an ultra-high frequency antenna system,receiving set and landing path indicator. By flying the airplane alongsuch a 2b path as to keep the deflection of the landing path indicatorconstant, the pilot comes down to ground on a curved line suitable forlanding. If the airplane rises above this line, the deflection of theindicator reads too high while if the airplane drops below this line,the deflection of the indicator reads too low.

Other and further objects of my invention will be apparent from thefollowing detailed description and the accompanying drawings. It is tobe expressly understood, however, that these drawings are for purposesof illustration only and are not designed for a definition of the limitsoi my invention. Referring to the illustrations,

Figure 1 is a drawing of typical transmitting equipment for producingthe landing beam.

Figure 2 shows a circuit diagram of one form of an ultra-high frequencyoscillator suitable for use in the transmitting system shown in Fig- 310ure 1.

Figure 3 shows a circuit diagram of an ultrahigh frequency receivingsystem suitable for use on the airplane in the detection of the radio- Ibeam signals.

Figure 3A shows a filter suitable for ouse in the arrangement oi Figure3.

Figure 4 is a drawing of the landing path indicator.

Figure 5 shows the directive characteristic of the landing beam in thehorizontal plane.

Figure 6 shows the vertical directive characteristics of the landingbeam.

Figure '1 shows a typical landing glide path obtained by the use of thissystem.

Figure 8 is a 3-dimensional view illustrating the use of the landingbeam in conjunction with means for horizontal guidance.

Figure 9 is a conventional showing of the radio receiver carried by theaircraft for detecting and indicating, preferably by an indicator 51,-

- cult and the antenna coupled thereto is shown in Figure 2. The numerali denotes a vacuum tube suitable for generating ultra-high fre- "quencyoscillations, 2 denotes a plate inductor, 30-

3 denotes a grid inductor, ii is a small air condenser, approximatelyequal to the interelectrode grid to plate capacity of the tube.connected in series to reduce the capacitance of the oscillatorycircuit, a condenser 3 is of relatively large capacity and connected inseries as a safety measure in case of flashoverof condenser Q, and 6, I,8 and 9 are suitable choke coils to keep the oscillatory current out ofthe power supply leads. The plate supply for the oscillator is securedby means of a step-up transformer. the secondary winding of which isconnected between the center tap of the filament transformer and theplate choke coil 9. The primary winding is connected to any suitablesource of A. C. power, such as the cycle supply mains. The use of A. C.supply permits the use of simple audio-frequency amplifying equipmentand filter system in the receiving equipment on the airplane as will beshown in connection with Figure 3. The radiating antenna iii isinductively coupled to the inductor 2 of the oscillatory circuit. Sincehorizontal antennas are used, the resultant radio beam is horizontallypolarized, requiring the use. of a horizontal receiving antenna on theairplane.

Referring to Figure 3 the detector tube ii contains a plate I? connectedto one-half of a doublet antenna it, a control grid it being connectedto the other half of the antenna i3 andto a grid-leak resistor 15. Thetube It also contains a filament it connected to a filament heatingbatter-y .il. and to the negative terminal of a plate battery it. Inaddition'to the above-mentioned elements it contains a screen grid l9-connected to the battery it. The plate 02 is also connected throughtheprimary of a transformer 20 to the positive terminal of the battery It.An amplifier tube 26 contains a plate 22 connected through the primarywinding of a transformer 23 to the battery it and a grid 26 connected toa filament 2% through the secondary winding of the transformer 2@. Thefilament heating .battery H for the filament it also supplies currentfor heating the; filament 25. The terminals of the secondary winding ofthe transformer it are connected to the A. 0. terminals of an oxiderectifier 26. The D. 0. terminals of the rectifiers are connected to alanding indicator 2! in series with a glide angle adjustment resistor28, the latter serving to control to some extent the angle of the glidepath. If desired, a mechanically tuned reed filter t9 consisting ofdriving coils 50 and pick-up coils 5i may be interposed between thesecondary winding of the transformer 23 and the oxide rectifier 26, asshown in Figure 3A. The reed 52 in this filter is tuned to the frequencyof the power supply to the plate of tube 2 of the transmitter, shown inFigure 2, and serves to exclude all extraneous frequencies while passingthe desired frequency. The four choke coils 29, 30, 3! and 32, aredesigned to keep the ultra-high radio frequency out of theaudio-frequency circuits of the receiving set. The method of coupling ofthe antennas to the electron tube and associated circuits in bothFigures2 and 3 may be as shown or through suitable transmission lines,which arrangements are known to the art.

The details of the landing beam indicator are shown in Figure 4. Itconsists of a D. C. microammeter 33 mounted on its side on the pilot'sinstrument board so that a pointer 33 moves vertically rather thanhorizontally. The deflection to be kept constant is chosen at half-scalereading, the instrument pointer being then in a horizontal position,coinciding with an arrow 35 marked On course. A rise of the-pointer 36above this position 35 indicates that the airplane is above the properlanding path, while the reverse is true if the pointer 36 falls belowthe arrow 35.

The operation of my invention will now be described. In Figure 5 thetransmitting equipment described in Figures 1 and 2 is shown located at36 and the horizontal directive characteristic of the radio'beamproduced is indicated by a graph 31. In the illustrations which followit will be assumed at all times that the airplane is guided along thedesired azimuthal direction of the landing beam by lateral guidingmeans.

In Figure .6 the transmitting equipment is shown located at 38 and thedirective characteristic of the radio beam produced in the verticalplane is indicated by a line 39. A dot and dash line to indicatestheline of maximum field intensity of the beam. This line is oriented atsuch an angle and the degree of vertical directivity of the beam 39 isso adjusted, that a glide path M will be suitable for a landing path forairplanes. Sixty-cycle -modulation of the landing beam transmitter isprovided to facilitate audio-frequency amplification at the receivingend. The airplanedoes not fly along an inclined axis (40 of the beam,but on the curved path M under the inclined axis whose curvaturediminishes as the ground is approached. The path M is the line of equalintensity of received signal below the axis of the beam. The diminutionof intensity as the airplane drops below the beam axis is compensatedbythe increase of intensity due to approachingthe beam transmitter."Thus, by flying the-airplane along such a path as tokeep the deflectionof the landing path indicator on the instrument board constant, thepilot comes down to ground on a' curved line suitable for landing. Tofacilitate its use by the pilot this instrument is mounted on its sideso that the pointer ,moves vertically rather than horizontally. Thedeflection to be kept constant is chosen at half-scale reading, theinstrument pointer being then in a horizontal position. A rise of thepointer above method of furnishing altitude indication.

this position indicates that the airplane is above the proper landingpath, while the reverse is true if the pointer falls below itshorizontal position. The indications of the position of the airplanerelative to the landing path are thus made readily comprehensible.

Several important advantages obtain for this The landing path may be sodirected as to clear all obstructions. The pilot following the landingpath is automatically kept above obstructions and no longer needs athorough knowledge of the terrain in order to effect a safe landing.Secondly, the landing path may be of different shape to suit diflerentlanding fields. This is of particular importance in getting into a smallfield." A third advantage lies in the fact that in the act of followingthe landing path, the pilot automatically "levels oif",*th'erebyfacilitating a) normal landing albeit somewhat fast. A' fourth advantageis that the landing glide may be begun at any desired altitude, within arather wide range (say, 500 to 5,000-feet) A fifth advantage arises fromthe ease of using the landing beam indications. No manipulations on thepart of the pilot are required. The tuning is fixed. Since a line ofconstant field intensity is followed no'control of volume is necessary.

A typical form of glide path is shown in Figure 7.

The field intensities are plotted as abscissas and altitude of theairplane as ordinates at each 1,000 feet of distance from the beamtransmitter. The data plotted were obtained experimentally, the fieldintensity being measured in terms of the deflection of the landing beamindicator. It will be observed that corresponding to this glide path apilot coming in at an altitude of 1,000 feet will observe half-scaledeflection of his instrument (250m) at a distance of approximately 9,000feet from the transmitter. If he then follows theline of constant fieldintensity-corresponding to halfscale deflection on his instrument, hereaches an altitude of 10 feet at a distance of 2.000 feet from the beamtransmitter. This is actually the point of contact of the airplane withthe ground, the receiving antenna being mounted on top of the airplane,10 feet from the ground.

The operations involved in landing an airplane through the use of thelanding beam are illustrated in Figure 8. While used in conjunction withother transmitters and devices, as noted before only the landing beamtransmitting and receiving system used alone or in combination with therunway and/or marker beacon comprises my invention. An airplane 42 isapproaching the landing field, being directed along the horizontal traceof the axis of a beam 43 by means of a runway localizing beacon id,which transmits the double-modulation signals 45, and is placed adjacentto a landing beam transmitter 46. As the airplane approaches the landingfield, the pointer of the landing beam indicator begins to rise tomidscale or horizontal position. When this position is reached, thepilot knows that he is on a point on the gliding path. To follow agliding path 47 he must maneuver the airplane to keep this pointer in a.horizontal position. It is necessary now that the pilot keep accuratelyon the runway course at the same time following down on the landingpath. About 100 feet from the landing-field boundary line the pilothears a marker beacon signal from a transmitter 48, which accuratelydefines the landing field bound- 75 ary. He is thus warned that thelanding point has nearly been reached and proceeds to follow the runwaybeacon course and the landing beam path to the point of landing. Infollowing the landing path prior to receiving the marker beacon signal,the pilot maintains an air speed somewhat above the landing speed of theairplane, insuring complete controllability with some margin to spare.Upon receiving the marker indication that he is passing over theboundary of the field, the margin over the landing speed may be reduced.The landing is therefore made at a speed more nearly approaching thenormal speed of the airplane.

The differently modulated beacon signals 45 are picked up by a radioreceiver 59 of the conventional type, the output of the receiver beingconnected to the filtering means 54, which may beeither of themechanically tuned type or of the electrically tuned type. At any ratethe filter 54 is to be of such means as will separate the two modulatedfrequencies of the beacon 44 and rectify the two separated frequenciesso that the resultant direct voltages connected in opposition to thecourse indicating microammeter 51 will furnish lateral guidance to thepilot by means of the needle 58.

A receiving apparatus for receiving the marker beacon signal is shown inFigure 10, which may be a standard radio receiver having ear-phones itconnected to the output thereof, or suitable indicating device.

The foregoing description comprehends only a general and preferredembodiment of my invention and changes in my method and details of myapparatus may be made within the scope of those claims which may beallowed, and therefore these claims are not intended as restricted tothe specific details of my invention as disclosed herein.

What I claim is:

1. A method of guiding aircraft approaching a landing surface whichconsists of transmitting a directive radio beam at a suitable angle withrespect to said landing surface, and guiding said craft to follow a.predetermined line of constant received signal below the angle ofmaximum radiation of the beam.

2. A method of guiding aircraft approaching a landing surface whichconsists of transmitting a directive radio beam at a suitable angle withrespect to the landing surface, and so guiding said craft that a line ofconstant received signal below the angle of maximum radiation of thebeam will be followed thereby traversing a path suitable for the properlanding of the craft.

3. A system for guiding in a vertical plane aircraft gliding to alanding surface which comprises means for transmitting from a groundstation a. signal radio beam directed upwardly at a fixed inclinedangle, means carried on aircraft responsive to said beam and meansactuated by said second mentioned means for indicating to the pilotdeviations in the vertical plane from a path along which the receivedenergy from the said radio beacon s in a predetermined amount at everypoint of glide.

4. In a system of guiding in a vertical plane aircraft gliding to ortaking off from a landing surfacewhich includes means for transmittingfrom a ground station a radio signal, the intensity of which signalincreases with altitude up to an altitude which makes an angle ofapproximately degrees between a straight line from said aircraft at saidaltitude to said ground station, and the horizontal radio receiving andsignal intensity indicating means on said aircraft responsive to saidsignal, said intensity indicating means being such as to indicate to thepilot of the-craft deviations of the aircraft in a vertical planerelative to a desired landing path.

5. In a system for blind landing or taking ofl of aircraft, acombination of a single radio beam directed at a vertical angle relativeto the land-' said instrument being such as to hold said position inregister with said index mark when said craft is gliding to or takingoff from the field in the proper path of flight in the sector of thebeam underlying the line of maximum transmission thereof and to indicatevertical deviation from said path.

6. A system of guiding in a vertical plane at a continually decreasingaltitude an aircraft approaching a landing surface comprising atransmitter emitting a single directive radio beam signal at a fixedinclined vertical angle with respect to said landing surface, a receiveron said aircraft responsive to said beam signal, an ,end zeropointer-type indicating instrument connected to the output of saidreceiver and responsive to the intensity of said beam signal, saidindicating instrument being mounted so that its pointer moves on avertical plane in front of a scale carrying an index mark in the centerof said scale, said pointer and said index mark coinciding during thegliding approach of said aircraft in said radio beam to said landingsurface.

.7. A method of guiding aircraft approaching a landing surface whichincludes transmitting a directive landing path course signal andfollowing said signal for lateral guidance, transmitting a directiveradio beam at a suitable vertical angle with respect to the landingsurface, and controlling the power radiated by said beam, following aline of predetermined received signal below the angle of maximumradiation of the beam, whereby the craft will follow a path suitable forthe proper landing of the aircraft.

8. A method of guiding in a vertical plane an aircraftgliding to ortakingofi from a landing area, which method includes projecting a beamof radiant energy with maximum radiant energy at a suitable verticalangle with respect to the landing area, receiving the radiant energyfrom the beam on the aircraft, holding the aircraft at such altitudesduring the period of reception of said "radiant energy on the craft thatsaid received radiant energy shall remain at a predetermined intensity.

9. A system for guiding aircraft approaching a landing surface whichincludes, in combination, means for transmitting from a ground station asignal beacon course, for lateral guidance of the aircraft to a landingpath, and another radio signal, the intensity of which increases withaltitude up to an altitude which makes an angle of approximately 20degrees between a straight line from the aircraft at said altitude tosaid ground station and the horizontal; radio receiving and signalindicating means on said aircraft responsive to said signals, one ofsaid indicating means being responsive to the field intensity of saidsecond signal for indicating to the pilot of the craft deviations of thecraft in a vertical plane relative to said landing path.

10. A system for guiding aircraft approaching a landing surface'whichincludes, in combination, means for transmitting from a groundstation a signal beacon course for lateral guidance of the aircraft to alanding path, and another radio signal, the intensity of which increaseswith altitude up to an altitude which makes an angle of approximately 20degrees between a straight line from the aircraft at said altitude tosaid ground station and the horizontal, radio receiving and signalindicating means on said aircraft responsive to said signals, one ofsaid indicating means being responsive to the field intensity of saidsecond signal for indicating to the pilot of the craft deviations of thecraft in a vertical plane relative to said landing surface, and meansfor transmitting a marker signal across said course for indicatingdistance to said landing surface.

11. A system for guiding l'aircraft approaching a landing surface whichincludes, in combination, means for transmitting from a ground station aradio beam directed at an inclined angle relatively to said surface,means for transmitting from said station an approach course signal forthe lateral guidance of the aircraft, means on the aircraft responsiveto the course signal and the field intensity of said beam, saidresponsive means including an indicator for indicating to the pilotdeviations in a vertical plane from the desired landing path.

12. A method of guiding in a vertical plane" an aircraft leaving alanding area which includes transmitting from a directive radio beamtransmitter a radio beam at an angle to the horizontal, receiving saidbeam on said aircraft, guiding said aircraft so that the signal receivedon said aircraft shall remain at a predetermined intensity during theperiod of climb.

13. A method of guiding an aircraft gliding to a landing area whichincludes flying into a signal defining a landing path and following saidsignal for lateral guidance; transmitting from a directive radio beamtransmitter a radio beam at an angle to the horizontal, receivingradiant energy from said beam on said aircraft, holding said aircraft atsuch altitudes that the radiant energy received on said aircraft fromsaid radio beam transmitter shall remain at a predeterminedintensity'until said aircraft makes contact with said landing area.

14. In a method for vertical guidance of an aircraft gliding to ortaking off from a landing surface whereby said aircraft may be guidedalong the proper vertical landing path which includes transmitting aradio beam from the ground at a vertically inclined angle, receivingsaid beam from said radio beam transmitter and following along the underhalf of said beam where the radiant energy received on the aircraft fromsaid beam is a predetermined value during the night to or from the saidlanding surface.

15. A method of guiding in a vertical plane an aircraft approaching ortaking ofi from a landing area which includes transmitting a radiosignal from a ground transmitting station of such a. character that theintensity increases with altitude, and receiving said signal on saidaircraft and holding said aircraft when landingat such decreasingaltitudes that the signal received on said aircraft from said groundtransmitting station shall remain at a predetermined intensity duringthe period of glide to said landing area and conversely when taking oil.

16. A method for guiding in vertical and horiaontal planes aircraftapproaching to and taking oif from a landing surface, which includestransmitting radiant energy, such as to produce on the aircraft asignal, the intensity of which is a function of the altitude of saidaircraft, and signals which give indications of the azimuthal 10position of said aircraft with respect to predetermined course inazimuth, receiving said radiant energy on said aircraft. guiding saidaircraft to and holding it at such altitudes that energy received fromsaid radiant source remains substantially at a predetermined intensity,and further guiding the aircraft to and holding it in an azimuthal planeto a position where the azimuthal signals received on said aircraft areof a predetermined relative intensity.

FRANCIS W. DUNMORE. 10

